C2SoftDav1dDec: Drain and signal resolution change based on seq header

When resolution change is detected based on seq header, drain all
the pictures from the decoder and signal resolution change.

This ensures output format change is signaled correctly when decoder
returns buffer corresponding to new resolution.

Bug: 317306503
Test: atest CtsMediaDecoderTestCases -- --module-arg \
CtsMediaDecoderTestCases:instrumentation-arg:\
codec-prefix:=c2.android.av1

Test: atest CtsMediaV2TestCases --  --module-arg \
CtsMediaV2TestCases:instrumentation-arg:codec-prefix:=c2.android.av1

Change-Id: I627380e916aa5bc3aa4b50e3396ade352ec60715